• Jeremy (2/2) Mar 27 2023 Is there a way I can define a manifest constant from the compiler
• ryuukk_ (52/54) Mar 27 2023 You can do this way:
• ryuukk_ (17/17) Mar 27 2023 I just remembered you can do something like this!

Jeremy <jtbx disroot.org> writes:

Is there a way I can define a manifest constant from the compiler 
command-line, like the -Dmacro option for C compilers?

ryuukk_ <ryuukk.dev gmail.com> writes:

On Monday, 27 March 2023 at 22:22:26 UTC, Jeremy wrote:
 Is there a way I can define a manifest constant from the 
 compiler command-line, like the -Dmacro option for C compilers?

You can do this way:


```
dmd -version=FEATURE_A
```

```D

import std.stdio;

void main()
{

     version(FEATURE_A)
     {
         writeln("feature A enabled");
     }

}

```

Unfortunatly there is not #ifndef, so in case you want to make 
sure FEATURE_A is not there you'll have to do:

```D

import std.stdio;

void main()
{

     version(FEATURE_A)
     {}
     else
     {
         writeln("feature A not available");
     }

}

```


or

```D

import std.stdio;


version(FEATURE_A)
{
     enum FEATURE_A_AVAILABLE = true;
}
else
{
     enum FEATURE_A_AVAILABLE = false;
}

void main()
{
     static if (!FEATURE_A_AVAILABLE)
     {
         writeln("feature A not available");
     }

}

```


For some reason they force us to be overly verbose

Or it's possible to do it, but i don't know much more than this 
about ``-version``


(if you use ldc compiler, it's ``-d-version=``)

ryuukk_ <ryuukk.dev gmail.com> writes:

I just remembered you can do something like this!


```
import std.stdio;

enum FEATURE_A_AVAILABLE()
{
     version(FEATURE_A) return true;
     else return false;
}

void main()
{
     static if (!FEATURE_A_AVAILABLE)
     {
         writeln("feature A not available");
     }

}
```

It's evaluated at compile time, so it's branchless!